Extensive studies during the past two decades have indicated that the pineal organ in vertebrates modulates several important time-dependent physiological processes. It has been shown that the pineal plays a significant role in the regulation of the reproductive physiology in mammals. Melatonin appears to be a principal hormone of the pineal. It has been repeatedly demonstrated that administration of melatonin to mammals effects the reproductive function, most probably by modulating pituitary gonadotropin secretion. However, it is becoming increasingly apparent that species variation places sharp limitation on the transfer of information to the understanding of pineal physiology to other animal types. Therefore, in order to understand the role of melatonin in human reproductive physiology, we propose its administration to human subjects. As a result of the very short half-life of melatonin in plasma and equally its rapid disappearance from the brain, it seems that infusing intravenously (IV) at a constant rate is probably the best way to maintain high concentrations. In a pilot study infusing melatonin intravenously and using our radioimmunoassay (RIA), we are the first to have demonstrated the ability to monitor the attainment of supra physiologic plasma concentrations. The objectives of this project are to examine the effects of an IV infusion of melatonin to human subjects in an attempt to demonstrate melatonin's anti-gonadatropic action. The experimental protocols in men and women are therefore designed to study melatonin's inhibitory effect on Luteinizing Hormone (LH) and Follicle Stimulating Hormone (FSH) secretion. Gonadotropin secretion is markedly increased in menopausal women. If melatonin is indeed anti-gonadotropic, its administration would be expected to lower gonadotropin levels in these women. Pituitary release of LH and FSH can be stimulated in men and women by administration of LHRH (LH releasing hormone). Melatonin will be administered to men, and to women at different phases of their menstrual cycle. If melatonin is anti-gonadal at the pituitary level, LH and FSH response to LHRH should be blunted. (Support for this view has recently been marshalled on animal studies.) Clomiphene has been shown to enhance gonadotropin secretion in men and women by acting as an anti-estrogen, presumably on the hypothalamus and possibly the pituitary as well. If melatonin administration decreases (Text Truncated -Exceeds Capacity)